The New York Stock Exchange said on Thursday it contacted American Home Mortgage Investment due to unusual market activity in the company's stock.
The exchange said in a statement posted on its Web site that it requested that American Home issue a statement indicating whether there are any corporate developments that may explain the unusual activity.
The exchange said American Home stated that its policy is not to comment on unusual market activity or rumors.
American Home's shares fell as much as 23.3% on Thursday on a rumor that a Wall Street investment firm had withdrawn a credit facility, analysts said.
American Home specializes in prime and "near prime" loans.
It has made many loans that allow borrowers to produce little documentation, which can be considered riskier.
American Home stock closed down almost 21% at $10.76.